Measures to prevent global warming have become an issue not for the distant future but for the near future, and green electricity, which generates little carbon dioxide, is being promoted as a means for suppressing the generation of greenhouse gases, which cause global warming. From the point of view of energy security, and out of concern regarding the current situation in which power generation relies on imports of crude oil from other countries, methods of supplementing power generation by means of sunlight, water power and wind power have been investigated on many fronts with the aim of securing energy that can be provided without external support, and some of those that have been proposed have been commercialized (for example photovoltaic power generation using solar panels, hydroelectric power using dams, propeller-based large-scale wind power generation).
Wind turbines have issues that need to be improved, in that blades that can rotate at high speed do not start rotating readily, while conversely blades that start moving under light wind do not rotate readily at high speed.
In order to improve the wind power utilization efficiency there exist methods for reducing the resistance of a wind turbine when it is moving against the airflow, using techniques in which small windows are opened, but these do not open completely. Thus wind which has exited does not flow out in the rearward direction until it has come into contact with a second wall, and therefore the degree of reduction in the resistance is small and turbulence of the rearward airflow increases.
There are also techniques whereby the resistance of a wind turbine is reduced when it is moving against the airflow by decreasing the surface area of the vanes using another motive force, but this has the complication that it requires a power source and the action of a mechanism to extend and retract the vanes, for example, for each rotation using an ‘on’/‘off’ type of relay, and as this must be performed for each cycle it is difficult for this to function when rotating at high speed.
Another means of airborne power generation uses a method in which a merry-go-round is pulled and caused to rotate, thereby generating electricity, by marine-leisure kites flown above the ground on a number of spindles which are extended when laid on the ground. This method has the problems that it cannot be performed in light wind, requiring wind that is stable and strong to a certain extent, and that each of the kites requires individual specialist handling, and a large area is required.
Another means of airborne power generation uses a system whereby electricity is generated by means of the rotation of an entire balloon, and thus equipment including a motor must be enclosed within the balloon, technical expertise is required in its manufacture, and maintenance is also complicated.
Savonius type wind turbines are characterized in that they generate high torque due to their large wind receiving area, but this is conversely a weakness in that it is difficult to implement countermeasures against strong winds such as typhoons.
There are other means of generating electricity using wind power which are implemented using a large-scale method whereby as a countermeasure against strong winds such as typhoons the wind turbine pylon itself is laid down in advance on the ground, but large losses are generated including stoppages for disaster avoidance.